Download cardiac impulse

12/10/11
Miss Radford
Control of the cardiac cycle
WAL: about how the cardiac cycle is regulated and
controlled.
Some
Most
All
• How are the sinoatrial node,
atrioventricular node and bundle of His
involved in controlling the cardiac cycle?
• What is myogenic stimulation of the heart?
• What are “cardiac output” and “stroke volume” and how
can these be calculated?
Your progress test on Cells will be on:
• Tuesday 3rd March
• Homework – revision and heart and
lungs sections of unit 1 booklets (due in
the following week) plus any left over
disease sections from the first part of
the booklet (due 10th March)!!
Today we are covering from the
specification:
Starter – refresh your mind
• Complete the heart structure worksheet to
recap how blood flows through the heart.
• Use the information sheet attached to help
you.
2. Which chambers of the heart have thicker walls?
3. Relate the thickness of the chambers to their
functions.
4. What is the function of the valves? Label the valves
on the diagram above.
5. What is the type of muscle that makes up the walls
of the heart? Why is it so special, and how does it
maintain a constant blood supply?
6. Trance the pathway a drop of blood would take
from the time it leaves the aorta, to the time it
returns to the left ventricle ready to leave the
aorta again, describing the chambers and vessels.
Challenge: can you write
these as numeric
equations?
Definitions
Heart rate = # beats
• Heart rate: number of heartbeats
per minute
minute
• Stroke volume: volume of blood (cm3) pumped by
heart in 1 beat
Stroke Volume = blood cm3
beat
• Cardiac output: stroke volume multiplied by the
3 Xblood
heart
rateOutput
gives the
amount
(cm=3)blood
pumped
Cardiac
= blood
cmof
# beats
minute minute
by heart in 1 minute beats
Get out your
calculators!
Heart rate
(beats/min)
Stroke
Volume
(cm3/beat)
At rest
75
75
During
exercise
180
120
Cardiac
Output
(cm3/min)
5,625
21,600
The Cardiac Cycle
•
•
•
•
•
Cardiac Cycle - The events of one heart beat
One cycle – 0.8 second (72 cycles a minute)
2 main processes – contraction and relaxation of the heart
muscle;
Diastole – lasts 0.5 seconds, represents the relaxation
phase, chambers fill with blood
Systole – lasts 0.3 seconds, represents the contraction
phase, blood pushed out of chambers/heart
The Heart’s
Conduction System
• The heart is myogenic
• This means it generates its own electrical
impulse
• The impulse that it generates is spread
throughout the heart and causes it to contract
• This is known as the cardiac impulse
The Spread of the
Electrical Impulse
• The impulse starts in the SA
Node (located at the top of
the right atrium)
• Called the pacemaker
• The impulse travels
through the atria walls
• This causes both atria to
contract
• The cardiac impulse then
reaches the AV node
• Also located in the right
atrium
• The AV node helps delay
the impulse to allow the
atria to finish their
contraction
• It then spreads the impulse
down the bundle of His
• This is located in the Septum
of the heart
• The bundle of His splits
into left and right
branches
• The impulse spreads
around the ventricle
walls through a network
of purkinje fibres
• This causes both
ventricles to contract
• The ventricles then relax
• The cycle is repeated
with the next cardiac
impulse
Cardiac Impulse
• http://video.about.com/heartdisease/Conduc
tion-System.htm
Q. Describe how the sinoatrial node (SAN) and the
atrioventricular node (AVN) control the increase in heart rate
during exercise
•
•
•
•
•
•
•
•
•
•
SAN initiates heart beat/sends impulses;
intrinsic/myogenic/pacemaker;
spread of impulses through atria;
atria contracts/systole;
impulse reaches AV Node;
Reduced delay of spread of impulses;
Bundle of His;
Purkinje fibres conducting impulses;
ventricular systole/contraction;
period of diastole/relaxation for filling;
Task – demonstrate your understanding
• Read pages 92 & 93 of your textbook.
• Answer questions 1 to 5.